High-energy irradiations have been used in several fields of application.
In the beginning the attention was on degradation processes of polymers. The chains were broken by high-energy irradiation with economical and ecological improvements and an exact process control via the dose was possible.
For instance, in the viscose process, studies on electron beam (EB) irradiation have been made by Fischer and Goldberg since 1980 (Patent DD 1 40747 and M. Lenzinger Ber., 1985, Issue 59, 32-39) and further investigation on the cellulose pulp were carried out by P. Burkart, (Polym. News, 1999, 24/6, 194-197). These studies opened a new route of commercial relevance to pulp activation in the viscose process which also has ecological advantages. With EB treatment on the cellulose pulp, degradation prevails by far on crosslinking and leads to a narrow chain length distribution and an enhanced accessibility of the cellulose, especially after alkali treatment.
More recently, the crosslinking route was investigated. In WO 01/30407, for example, a polyvinyl alcohol solution in water, containing natural polymers, can be cross-linked using high-energy irradiation to form hydrogels for use in the medical field; the products obtained by this process are described as having qualities of sterility, transparency, cooling effect, biocompatibility, oxygen permeability, absorption, humid environment.
The introduction of functional groups on the polysaccharide chain has been another object of several studies. In particular, studies have shown that it is of great importance the etherification and esterification of cellulose with functional groups to obtain fibers with improved qualities of resistance and applicability.
For instance, an esterification process for preparing polyanhydride cross-linked fibrous cellulosic products is claimed in WO 98/13545 [Amoco Corporation].
However a significant drawback of the esterified and etherified functional derivatives that makes them less attractive from a practical viewpoint is the low stability of ester bonds: in fact they are cleaved under alkaline conditions, as usually happens by repeated laundry, especially with strong detergents.
It is important to obtain functionalization of polysaccharides with functional groups that have stable bonds which, for example do not break in alkaline conditions, so that the polysaccharide does not degrade easily after it is washed with detergents.
European patent application 01830331 discloses a process to functionalize linen by introducing a stable bond at the O of the hydroxyl groups of the polysaccharide structure maintaining the allomorph I state.
However the state of the art does not report any example of functionalizing a polysaccharide by the formation of stable carbon-carbon bonds on the polysaccharide chain.